The question of whether a cashew is a nut or a fruit highlights the difference between scientific classification and common culinary language. The cashew plant produces two distinct structures, each with a different botanical identity. Understanding the cashew’s unique anatomy requires looking beyond the typical definitions of nuts and fruits.
The Botanical Reality of the Cashew Plant
The cashew tree (Anacardium occidentale) yields a double structure starting with the cashew apple. This large, colorful, pear-shaped body is not the true fruit. It is a swollen structure that develops from the flower stem and receptacle. Botanists classify the cashew apple as an accessory fruit because the fleshy, edible part is derived from tissue adjacent to the ovary, not the ovary itself.
The true fruit is a small, kidney-shaped shell, technically a drupe, which hangs from the bottom of the accessory fruit. A drupe is a type of fruit characterized by a single seed encased in a hard, stony layer, similar to a peach or an olive. The edible portion sold commercially is the seed found inside this hard drupe shell. The cashew consumed is therefore botanically a seed housed within a true fruit.
Culinary Definitions vs. Scientific Classification
The widespread reference to the cashew as a “nut” stems from its commercial characteristics, disregarding its botanical origins as a drupe seed. In the world of commerce and cooking, the term “nut” is applied to any large, oily kernel used in food preparation. This broad culinary category includes items like almonds, pecans, and pistachios, which are also botanically classified as drupe seeds, not true nuts.
A true nut, in the strict botanical sense, is a dry, indehiscent fruit with a woody shell that does not open to release its single seed upon maturity, such as an acorn or a hazelnut. Because the edible cashew seed is extracted from a drupe, it does not meet this specialized definition. The acceptance of the cashew as a tree nut is based purely on its texture, high fat content, and shared usage with other culinary nuts.
Essential Processing for Consumption
Unlike many other commonly consumed kernels, the cashew cannot be safely eaten straight from the tree. The shell of the true fruit contains a potent, caustic oil called urushiol, which is the same toxic chemical found in poison ivy and poison oak. Contact with this substance causes severe skin irritation in humans, and ingesting it can lead to serious internal reactions.
To neutralize this toxin, harvested cashews must undergo a rigorous high-heat treatment process, typically involving steaming or roasting. This heat breaks down the urushiol before the hard outer shell is cracked and removed. The process ensures that any cashews purchased in stores, even those labeled “raw,” have been heat-treated and shelled to eliminate the toxic residue, making them safe for consumption.